Lung inflammation and alterations in endothelial permeability play a major role in the pathophysiology of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), the conditions associated with high mortality rates. Low efficiency of current therapies may be explained in part by focus on drug treatments aimed at prevention of the onset of ALI, while endogenous feedback mechanisms which subside inflammatory activation and endothelial barrier dysfunction, although much more clinically relevant, remain poorly understood. Our studies in the previous cycle identified a novel role of microtubule peripheral network in the control of lung endothelial barrier function. We discovered that stimulation of microtubule peripheral growth by barrier enhancing agonists, such as hepatocyte growth factor, promoted Rac GTPase-dependent and attenuated Rho GTPase-dependent signaling, thus leading to downregulation of vascular leak. We defined a novel paradigm of dual regulation of Rac and Rho pathways by microtubule-associated guanine nucleotide exchange factors Asef and GEF-H1 and demonstrated essential role of the microtubules in the mechanisms of Rac-Rho crosstalk and control of endothelial permeability. However, the entire mechanism of microtubule-dependent regulation of onset and resolution of ALI, and specifically, microtubule-dependent modulation of inflammatory cascades, remains poorly understood. During the screening of potential signaling proteins associated with the microtubules in control and inflamed pulmonary endothelium, we discovered an association of a negative regulator of inflammatory signaling, SOCS1, with the microtubule fraction. This serendipity finding suggested a novel link between the microtubule cytoskeleton and control of endothelial inflammation and inflammation-induced permeability. Currently, a role of microtubules in the modulation of endothelial barrier response to bacterial wall compounds, cytokines, etc., remains virtually unknown. We hypothesize that cellular feedback mechanisms modulating cell inflammatory response critically require microtubule-assisted SOCS1 targeting to the submembrane compartment, where it interacts with its cytokine receptor- and TLR-associated protein targets. Using cell, ex vivo, and in vivo models of LPS-induced ALI this application will characterize regulation of LPS-induced inflammation by SOCS1, investigate involvement of microtubules in control of SOCS1 anti-inflammatory function, and will identify molecular mechanisms of active microtubule-assisted SOCS1 transport and submembrane targeting. The results of this project will delineate novel microtubule-dependent mechanisms regulating lung barrier dysfunction and inflammation, which may lead to discovery of a new group of pharmacological molecules for the treatment of ALI/ARDS.